Applicability of impulse noise hearing damage risk criteria (DRCs) to hearing protectors

Abstract

Hearing damage risk criteria, DRC, concerning exposure to impulse noise, developed by CHABA [Ward CHABA Report (1968)], Pfander [J. Acoust. Soc. Am. 67, 628–633 (1980)], Smoorenburg [New Perspectives on Noise] (Raven, New York, 1982), pp. 471–490], and Dancer [Acust. Acta Acust. 3, 539–547 (1995)], have been destined for impulses encountered in open space, in free-field conditions. To adapt these criteria for conditions in which hearing protective devices (HPDs) are used, a standard procedure was proposed in the literature (e.g., by Pfander) that consists in subtracting the attenuation of the HPD, typically 25 dB, from the impulse’s peak SPL. Such a simple method does not take into account the change of the signal waveform under the HPD, usually resulting in increased A, C, or D duration. In this study, the subtraction method was verified by a comparison of impulse noise DRC with the parameters of acoustic impulses measured under the earmuff: peak SPL, rise time, and A, C, and D duration. Results show that the subtraction method underestimates the possible hearing damage risk posed by exposure to impulse noise when a hearing protector is used. [Work supported by the Polish Ministry of Science and Education, Grants T07B00428 and SP03.1].